1. Field of the Invention
The present invention relates to a semiconductor device with a fuse. More particularly, it relates to fuses (i.e., fusible links) of a programmable read-only memory or a dynamic random-access memory having a redundant organization.
2. Description of the Prior Art
A number of fuses are provided in a semiconductor memory device. In the case of a programmable read-only memory, the fuses are used in the writing of information. In the case of a dynamic random-access memory having a redundant organization, the fuses are used to replace defective memory elements with redundant (spare) rows or columns. The fuses are formed of, e.g., polycrystalline silicon, and are electrically blown by an excess current pulse. Since the fuses are, generally, covered with a film (i.e., a passivation film) of phosphosilicate glass or silicon dioxide, the blown parts of the fuses are in the vicinity of each other and, in some cases, may not completely separate from each other, depending on the circumstances. Furthermore, when a fuse covered with a phosphosilicate glass film is blown, the film becomes opaque, thereby making it difficult to determine with a microscope whether or not the fuse is completely blown. It is possible to blow a fuse with a high-power laser. In such a case, however, a portion of the fuse and a portion of the covering film on it simultaneously melt and evaporate, thereby forming a hole which must be filled with phosphosilicate glass or silicon dioxide.